The U.S. Pat. No. 5,262,748 discloses an electric switch comprising a slot located between the housing and the surface housing, which are joined together. Located pivotally over the slot is a press block which is provided at one end thereof with a linking piece. The slot is provided at the bottom thereof with three sets of wire connecting pieces. Two of the three sets of wire connecting pieces are provided respectively with a platinum connection point and contact spring piece having one end which extends to reach over another wire connecting piece and which is also provided with a platinum connection point capable of making contact with the platinum connection point of another wire connecting piece. The one end of the contact spring piece is connected with the lower end of the linking piece so as to link the press block with the contact spring piece.
When an electric current becomes excessive, the surface curvature of the contact spring piece is caused to change so as to interrupt dutomatically the flow of the electric current.
The prior art switch described above is defective in design in that the contact spring piece is susceptible to a deformation caused by the temperature fluctuation. In other words, the metal fatigue of the contact spring piece can result in the instability of temperature sensitivity of the contact spring piece, thereby undermining the precision with which the contact spring piece responds to the fluctuation of temperature. As a result, the automatic interruption of the flow of the electric current can be brought about erroneously.